Proper way to adjust timing?

[32433s10]

Trying to learn what the best and proper way to adjust the main timing table. I've been doing some searching and can't find a solid answer on how it's done. Do you log spark advance if you do what do you do with it after the log? I know how to log KR but is the proper way to adjust it, is to copy that histogram and subtract it from main spark table? I'm try to learn so bear with me please..

[Firebirdmuscle]

Trying to learn what the best and proper way to adjust the main timing table. I've been doing some searching and can't find a solid answer on how it's done. Do you log spark advance if you do what do you do with it after the log? I know how to log KR but is the proper way to adjust it, is to copy that histogram and subtract it from main spark table? I'm try to learn so bear with me please..

I've always read where the best and proper way to do timing is on a loaded dyno where you can dial in each cell at the highest timing value that makes the most power for th current set of mods that you have done.

[32433s10]

I did read the same thing somewhere myself. There has to be another way I mean not everyone has access to one.

[schpenxel]

There really isn't a better way to do it. Too much timing or too little timing, both will give you less torque and thus less rwhp. People misunderstand and think more timing is always better as long as you don't get knock.. that just isn't always true. You want peak cylinder pressure to happen at the right point, around 15* after TDC. It happening after that wastes some of the energy, it happening before that puts a shit ton of force on the piston/rods and does nothing to help actually spin the crankshaft. Think about it.. Try pushing a piston down from exactly TDC vs. one that's 15* after TDC. At TDC all of the energy is pushed down through the piston/rod/bearing/crank instead of being used to rotate the crank.

Most people will just advance timing until you start to get some knock then back it off a few degrees. That's about the best you can do without a dyno though.

[mowton]

The closer you get to cylinder Peak Combustion Pressure, the more efficient the power stroke and the energy you will develop to the crank. If you don't have a dyno to record the torque, then try logging data that will "time" acceleration to a specific mph. That way as you make changes to the timing, you can determine if you are improving or reducing power by the time it takes to bet to your predetermined parameter. Its a matter of baseline vs new, not the absolute parameter.

Here is an expert from our tutorial on the effects of timing and power ....


Module 1 -- ERM Performance Tuning EFI Engine Management Overview Rev C -- 12/07/15


........Now that we have the right proportions for the "cake", we need to "cook" it.....in comes the ignition spark. Like everything else, the spark has its right and wrong time to enter the party! Too early and the piston is going to be very unhappy and too late and the Torque levels will suffer. One thing you need to understand is the ignition point is not an explosion. It is a controlled burn with an expanding flame front which is increasing the pressure in the cylinder in a linear fashion as it moves towards the piston. The piston on the other hand is rising towards the cylinder head and decreasing the volume of the cylinder which increases the pressure in the cylinder as well. The point that these two increasing pressures meet can be the difference between Maximum Brake Torque (MBT) or grenading a piston!!!! If the piston is moving up in its compression stroke and the flame fronts expanding pressure reaches it too soon, then the piston will be subjected to increasing downward forces which will actually try and slow it down. The goal is to time your ignition so this meeting point is as close to TDC as possible while attaining a maximum cylinder pressure or Peak Combustion Pressure (PCP) at 16 crank degrees ATDC. This is the point where you will impart maximum leverage to the crank through the piston/connecting rod thus developing MBT. To soon and you will experience a very forceful collision which at best will create pinging/knock or at worse case a broken ring land/piston and all the carnage that goes with that. Concurrently, if the piston has begun its downward travel, then the flame fronts expanding pressure will essentially be chasing the piston and will develop much lower torque. The advance of the spark has to support a burn rate that arrives at the above criteria across the entire RPM range. This is why, as the rpm increases (less time to reach PCP) the more advanced your timing needs to be.

If you could be inside the cylinder during the compression/power stroke it could go something like this:

1. Cylinder charge has been ingested into cylinder and the piston begins its upward journey (compression) to TDC
2. This upward travel begins to increase the pressure within the cylinder (both valves should be closed at this time) by compressing the cylinder charge and decreasing the cylinder volume
3. The timing of the spark to initiate the burn then can go 3 ways:
   
   • Get a late start, the piston will have gone beyond its MBT point and will actually be traveling in its downward (Power stroke) direction ahead of the expanding pressure from the flame front. As such, the cylinder volume will be increasing ahead of the flame fronts expanding pressure producing less power
   • Get an early start, the piston will be before its MBT point and will still be traveling in its upwards direction (compression stroke), increasing cylinder pressure through compression but in its way before reaching the magical 16 degrees, is the expanding pressure from the flame front and they meet head on with an impact! This impact slows the rising piston thus reducing its power.
   • Get the timing advance correct and as the piston is traveling in its upwards direction (increasing cylinder pressure), the expanding pressure from the flame front meets with the compression's pressure with the least amount of braking (pumping efficiency) and increases in pressure in advance of the increasing cylinder volume of the piston in its downward travels (Power stroke) thus imparting the maximum amount of leverage on at the crankshaft.

[32433s10]

That makes a lot of sense. I do know to make peak power you need a dyno. I'm just trying to get a idea on what are some way to adjust the timing what the pros do when they, lets say if they do a street tune. Should you worry about WOT advance in them situations and not really the idle and part throttle areas. I'm just used to a distributor and how simple they are with a curve and max timing at WOT.

[Pekka_Perkeles]

It's not just the WOT that needs to be taken care of.

If you don't dial the part throttle, you may have overheating issues, bad fuel economy or just hot underhood temps.

Now, with $79,99 EGT sensor you would at least to get a hint what's your engine doing in various situations.

http://www.plxdevices.com/EGT-Exhaus...7346002184.htm

Just log it and go from there.